The prior application Ser. No. 08/011,323 filed Jan. 29, 1993 (referred to above) disclosed and discussed the stepped wavefront output which can be produced by certain angles of scan and by certain positions of scan in scanning microlens array apparatus. A stepped wavefront output at the outlet of the scanning microlens arrays can result from differences in the lengths of the optical paths that the segments of the incoming wavefront must travel in the air in front of the microlens arrays before the segments are transmitted through the individual unit cell trains in the microlens arrays.
Each unit cell train can be constructed to transmit, within the unit cell train, a segment of the incoming wavefront. Each segment transmitted within an individual unit cell train is polychromatically correct within the transmitted segment and also has a collimated output without any steps in that segment at the outlet of the individual unit cell train. Each unit cell train provides a collimated output through the exit pupil of the unit cell train without vignetting. These characteristics of each individual unit cell train are true for all angles of scan of an individual unit cell train. This is illustrated in FIGS. 12-16 of said application Ser. No. 08/011,323 and is discussed in the description relating to those figures of the drawings.
However, when the unit cell trains are mounted in rows and columns in rectangular arrays, and when the scanning array of microlenses is moved (in a direction aligned with the columns) to a scan position in which the angle of scan (theta, .theta.) is an angle inclined to the optical axis (when the incoming wavefront is viewed at an angle other than head on), the segment of the wavefront transmitted to each unit cell train in a column of unit cell trains will have an optical path length (in the air in front of the arrays) which is different from the optical path length of every other unit cell train in that column. The differences in the lengths of the optical paths in the air in front of the arrays produce steps in the wavefront at the output of the arrays. This occurs, even though (as noted above) each individual segment of the wavefront transmitted through each individual unit cell train in the column is transmitted through that individual unit cell train collimated and without any optical path length differences in that individual segment of the wavefront.
FIG. 22 of said application Ser. No. 08/011,323 illustrates this phenomenon.
As illustrated in FIG. 22 of said application Ser. No. 08/011,323, the entire wavefront as transmitted through the scanning microlens arrays does have steps in the wavefront at the outlet of the arrays.
FIG. 22 of said application Ser. No. 08/011,323 shows the steps which are present in the output wavefront when the scanning microlens array is positioned to produce a plus 20 degree angle of scan.
As described in said application Ser. No. 08/011,323, if the incoming light is monochromatic light and if the scanning microlens array is positioned at an Eigen angle location, then the steps in the mosaic wavefront (which steps result from the differences in the lengths of the optical paths of the segments of the wavefront in the air in front of the arrays) have a particular monochromatic diffraction point spread function response at the detector plane which produces a single high intensity peak for each pixel corresponding to each unit cell train. Satisfactory image resolution is possible and is obtained under these conditions. In this monochromatic light, Eigen angle scan location, mode of operation, the scan may be either in an X direction or in a Y direction, or the scan may be a two dimensional scan in both the X and Y directions.
Thus, if each position of scan of the scanning microlens array is an Eigen angle position for the particular wavelength of the monochromatic light transmitted through the scanning microlens array apparatus, the monochromatic diffraction point spread function point spread response in each pixel will be a high intensity, single peak as illustrated in FIG. 32 of said application Ser. No. 08/011,323; and satisfactory imaging at the detector plane is obtained.
However, for polychromatic light, wavefront correction of the stepped wavefront is needed in order to produce acceptable imaging for the polychromatic light. This is pointed out at page 34, lines 13-16 of said application Ser. No. 08/011,323.
The steps must be removed to obtain acceptable imaging for polychromatic light.